Mozilla/5.0 (Windows NT 6.1; WOW64; rv:13.0a1) Gecko/20120212 Firefox/13.0a1 STR (requires dual monitor setup): 1. Load http://pearce.org.nz/full-screen/ 2. Press 'f' key to enter fullscreen. 3. Click on the desktop in your other monitor, fullscreen will exit. 4. Focus the browser window again and press 'f', a fullscreenerror will be thrown. In the webconsole the following error is logged: "Request for full-screen was denied because requesting element is not in the currently focused tab." Problem doesn't occur in FF10.0.1 [Mozilla/5.0 (Windows NT 6.1; WOW64; rv:10.0.1) Gecko/20100101 Firefox/10.0.1], though I can't focus the chrome UI after following the STR above (possibly related to 718939?).
Regression range: http://hg.mozilla.org/mozilla-central/pushloghtml?fromchange=d75ebb37080e&tochange=2afd7ae68e8b Most likely a regression from bug 706672, which merged to m-c in that range.
This should be fixed by bug 706672.